Urea is made primarily by reacting carbon dioxide with anhydrous ammonia at high pressure and temperature and with removal of by-product water (dehydration). The resulting molten material can be processed into prills or granules for use as a fertilizer. Normally, the granular form is somewhat larger in particle size than the prills.
Urea, whether granulated or prilled, (which together hereinafter will be referred to in combination as a granular-type urea) is one of the most widely used fertilizers. Urea is a white crystalline solid under normal ambient conditions containing 46% nitrogen. Urea is highly water soluble.
Urea has a number of recognized advantages relative to other nitrogen fertilizers. Urea is safer to ship and handle than for example ammonium nitrate. Urea is less corrosive to equipment than for example ammonium sulfate. Because urea has a higher nitrogen content than these other nitrogen-based fertilizers, urea also supplies more nitrogen per ton of applied solids.
While the prior art has proposed a variety of ways for producing granular-type urea fertilizers, the prior art has not successfully provided a primarily urea-based fertilizer with an extended-release nitrogen component. Thus, there remains a continuing need for a new granular-type urea fertilizer having extended-release nitrogen.